The summary says it all. If you emerge xawtv without emerging xset first the build will fail when the xawtv makefile calls xset. This is only when using the new modular X.org (7.0+).
<snip> RDEPEND=">=sys-libs/ncurses-5.1 >=media-libs/jpeg-6b media-libs/libpng X? ( || ( ( media-libs/fontconfig x11-libs/libFS x11-libs/libICE x11-libs/libXpm x11-libs/libXmu x11-libs/libX11 x11-libs/libXaw x11-libs/libXt x11-libs/libSM x11-libs/libXft x11-libs/libXext x11-libs/libXrender xext? ( x11-libs/libXinerama x11-libs/libXxf86dga x11-libs/libXrandr x11-libs/libXxf86vm ) x11-apps/xset <---- HERE! xv? ( x11-libs/libXv ) ) virtual/x11 ) ) ... DEPEND="${RDEPEND} ... </snip> *** This bug has been marked as a duplicate of 131673 ***